1. Field of the Invention
The present invention relates to a rotational phase adjusting apparatus for adjusting opening/closing timings (a valve timing) of intake valves and exhaust valves of an internal combustion engine (an engine) in accordance with engine operating conditions.
2. Related Art
As a conventional valve timing adjusting apparatus for adjusting valve timing of intake valves and exhaust valves of an engine, a vane-type driving force transmitting member which transmits a driving force from a crankshaft as a driving shaft of the engine to a camshaft as a driven shaft is known. The vanes are accommodated relatively turnably within a housing, and the phase difference of the vanes against the housing is controlled by fluid pressure of operating fluid or the like. It is considered that the housing has a construction wherein a circumferential wall is integrally formed with one side wall so that possibility of leakage of the operating fluid from a fluid pressure chamber is reduced and assembling work is simplified.
The housing having the circumferential wall integrally formed with one side wall requires machining accuracy of an inside surface, an inner circumferential surface, and an opening end surface opposite to the integrally-formed side wall especially in the following points (1), (2) and (3).
(1) Inside surface, inside circumferential surface: sealability among the fluid pressure chambers
(2) opening end surface: leakage of the operating fluid to the outside of the housing
(3) Depth from the opening end surface to the inside surface: sealability due to clearance with a vane, and scoring and uneven wear due to sliding with the vane
The housing is required to be machined with high accuracy: for example, surface roughness to within 3.2 to 6.3 z, depth accuracy to 20 .mu.m, squareness between the inner circumferential surface and the inside surface to 10 .mu.m, and flatness of the opening end surface and the inside surface to 20 .mu.m. To achieve the machining with high accuracy, it is necessary to machine working surfaces of the housing, i.e., the inside surface, the inner circumferential surface and the opening end surface opposite to the integrally-formed side wall by clamping without reclamping, and to suppress deformation due to clamping as least as possible.
A general clamping method by which the peripheral wall of the housing is pressed inward radially makes it possible to cut above-described all working surfaces by clamping without reclamping; however, this causes large deformations of the housing if a hollow member with a thin-walled portion like a vane-type housing is pressed inward radially.
As shown in FIGS. 16 and 17, it is considered that clamp seats 122 and 132 are provided in housing 120 and 130 respectively, and the housing 120 and 130 are axially pressed by a clamp 125 in contact with the clamp seats 122 and 132. When using this clamping method, opening end surfaces 121a, 131a, inner circumferential surfaces 121b, 131b and inside surfaces 123, 133 can be machined by clamping without reclamping. In case where the clamp seats 122 and 132 are provided in the outer periphery of thin circumferential walls 121 and 131 respectively and are pressed, resilient deformations of the housings 120 and 130 due to pressure become large as shown with chain double-dashed lines in FIGS. 16 and 17. Though the deformation is recovered by removing the clamp 125 after machining, the flatness of the opening end surfaces 121a and 131a, the squareness between the inner circumferential surface 121a and the inside surface 123, and that between the inner circumferential surface 131a and the inside surface 133 are degraded.
As in a method of machining a revolving scroll disclosed in JP-A 6-712, a peripheral groove and a radial groove may be formed in the outer peripheral wall of an end plate so that deformation when clamping is reduced. In the case of the vane-type housing, however, the housing stiffness is decreased if the peripheral groove is formed because a part of the outer peripheral wall does not protrude outward radially unlike the end plate. Though wall thickness may be increased or a ring-shaped jaw portion for forming the peripheral groove may be formed, this increases the size of an apparatus. Furthermore, this causes a problem of complicated machining of the peripheral groove and the radial groove.